The alkaline earth carbonates are an important class of minerals. This volume compiles and critically evaluates solubility data of the alkaline earth carbonates in water and in simple aqueous electrolyte solutions. Part 1, the present paper, outlines the procedure adopted in this volume in detail, and presents the beryllium and magnesium carbonates. For the minerals magnesite (MgCO 3 ), nesquehonite (MgCO 3 Á3H 2 O), and lansfordite (MgCO 3 Á5H 2 O), a critical evaluation is presented based on curve fits to empirical and=or thermodynamic models. Useful side products of the compilation and evaluation of the data outlined in the introduction are new relationships for the Henry constant of CO 2 with Sechenov parameters, and for various equilibria in the aqueous phase including the dissociation constants of CO 2 (aq) and the stability constant of the ion pair MCO 0 3 ðaqÞ (M ¼ alkaline earth metal). Thermodynamic data of the alkaline earth carbonates consistent with two thermodynamic model variants are proposed. The model variant that describes the Mg 2þ ÀHCO À 3 ion interaction with Pitzer parameters was more consistent with the solubility data and with other thermodynamic data than the model variant that described the interaction with a stability constant.
Snow and rain samples collected in Sendai, Japan, were analyzed for sodium, potassium, magnesium, calcium, and strontium. The chemical composition of the samples can be fairly explained by adding some calcium to diluted seawater. A low Sr/Ca ratio in most of the samples showed that the excess calcium over seawater contribution may be derived from calcite contained in soil dust transported by wind from North China.
The mechanism of phosphate coprecipitation with calcite is proposed on the basis of homogeneous distribution of phosphate in the crystal at 20°C and pH 7.9-9.5. At a constant pH, phosphate content of calcite is proportional to total phosphate concentration in aqueous solution. PO' ions are uptaken into the calcite lattice, where 3 CO3 ions are replaced by 2 P04 ions in aqueous solution, as described by the ion exchange equilibrium:where S and L represent calcite and aqueous solution, respectively.
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